2,149 research outputs found
Non-topological solitons in brane world models
We examine some general properties of a certain class of scalar filed theory
models containing non-topological soliton solutions in the context of brane
world models with compact large extra dimensions. If a scalar field is allowed
to propagate in extra space, then, beside standard Kaluza-Klein type
excitations, a whole new class of very massive soliton-type states can exist.
Depending on their abundance, they can be important dark matter candidates or
give significant contribution to entropy and energy density in our universe. .Comment: version accepted for publication in Physical Review
Degradation and healing in a generalized neo-Hookean solid due to infusion of a fluid
The mechanical response and load bearing capacity of high performance polymer
composites changes due to diffusion of a fluid, temperature, oxidation or the
extent of the deformation. Hence, there is a need to study the response of
bodies under such degradation mechanisms. In this paper, we study the effect of
degradation and healing due to the diffusion of a fluid on the response of a
solid which prior to the diffusion can be described by the generalized
neo-Hookean model. We show that a generalized neo-Hookean solid - which behaves
like an elastic body (i.e., it does not produce entropy) within a purely
mechanical context - creeps and stress relaxes when infused with a fluid and
behaves like a body whose material properties are time dependent. We
specifically investigate the torsion of a generalized neo-Hookean circular
cylindrical annulus infused with a fluid. The equations of equilibrium for a
generalized neo-Hookean solid are solved together with the convection-diffusion
equation for the fluid concentration. Different boundary conditions for the
fluid concentration are also considered. We also solve the problem for the case
when the diffusivity of the fluid depends on the deformation of the generalized
neo-Hookean solid.Comment: 24 pages, 10 figures, submitted to Mechanics of Time-dependent
Material
Spatial and frequency domain effects of defects in 1D photonic crystal
The aim of this paper is to present the analysis of influence of defects in
1D photonic crystal (PC) on the density of states and simultaneously
spontaneous emission, in both spatial and frequency domains. In our
investigations we use an analytic model of 1D PC with defects. Our analysis
reveals how presence of a defect causes a defect mode to appear. We show that a
defect in 1D PC has local character, being negligible in regions of PC situated
far from the defected elementary cell. We also analyze the effect of multiple
defects, which lead to photonic band gap splitting.Comment: presented at International Workshop on Physics of Photonic Crystals
and Metamaterials, Brussels, Belgium, 12-13.06.200
Enhanced Luminescence of InGaN / GaN Vertical Light Emitting Diodes with an InGaN Protection Layer
We have investigated the effectiveness of a thin n-In0.2Ga0.8N layer inserted in the bottom n-GaN layer
of InGaN/GaN blue light emitting diodes (LEDs) for the protection of multiple quantum wells during the
laser lift-off process for vertical LED fabrication. The photoluminescence properties of the InGaN/GaN
lateral LEDs are nearly identical irrespective of the existence of the n-In0.2Ga0.8N insertion layer in the
bottom n-GaN layer. However, such an insertion is found to effectively increase the photoluminescence
intensity of the multiple quantum well and the carrier lifetime of the vertical LEDs. These improvements
are attributed to the reduced defect generations in the vertical LEDs during the laser lift-off process due to
the presence of the protection layer.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3521
The application of componentised modelling techniques to catastrophe model generation
In this paper we show that integrated environmental modelling (IEM) techniques can be used to
generate a catastrophe model for groundwater flooding. Catastrophe models are probabilistic models
based upon sets of events representing the hazard and weights their likelihood with the impact of such
an event happening which is then used to estimate future financial losses. These probabilistic loss estimates
often underpin re-insurance transactions. Modelled loss estimates can vary significantly, because
of the assumptions used within the models. A rudimentary insurance-style catastrophe model for
groundwater flooding has been created by linking seven individual components together. Each component is linked to the next using an open modelling framework (i.e. an implementation of OpenMI). Finally, we discuss how a flexible model integration methodology, such as described in this paper, facilitates a better understanding of the assumptions used within the catastrophe model by enabling the interchange of model components created using different, yet appropriate, assumptions
A contingency analysis of LeActiveMath's learner model
We analyse how a learner modelling engine that uses belief functions for evidence and belief representation, called xLM, reacts to different input information about the learner in terms of changes in the state of its beliefs and the decisions that it derives from them. The paper covers xLM induction of evidence with different strengths from the qualitative and quantitative properties of the input, the amount of indirect evidence derived from direct evidence, and differences in beliefs and decisions that result from interpreting different sequences of events simulating learners evolving in different directions. The results here presented substantiate our vision of xLM is a proof of existence for a generic and potentially comprehensive learner modelling subsystem that explicitly represents uncertainty, conflict and ignorance in beliefs. These are key properties of learner modelling engines in the bizarre world of open Web-based learning environments that rely on the content+metadata paradigm
Functional characterization of three genes encoding putative oxidoreductases required for cercosporin toxin blosynthesis in the fungus Cercospora nicotianae
Cercosporin is a non-host-selective, photoactivated polyketide toxin produced by many phytopathogenic Cercospora species, which plays a crucial role during pathogenesis on host plants. Upon illumination, cercosporin converts oxygen molecules to toxic superoxide and singlet oxygen that damage various cellular components and induce lipid peroxidation and electrolyte leakage. Three genes (CTB5, CTB6 and CTB7) encoding putative FAD/FMN- or NADPH-dependent oxidoreductases in the cercosporin toxin biosynthetic pathway of C. nicotianae were functionally analysed. Replacement of. each gene via double recombination was utilized to create null mutant strains that were completely impaired in cercosporin production as a consequence of specific interruption at the CTB5, CTB6 or CTB7 locus. Expression of CTB1, CTB5, CTB6, CTB7 and CTB8 was drastically reduced or nearly abolished when CTB5, CTB6 or CTB7 was disrupted. Production of cercosporin was revived when a functional gene cassette was introduced into the respective mutants. All ctb5, ctb6 and ctb7 null mutants retained wild-type levels of resistance against toxicity of cercosporin or singlet-oxygen-generating compounds, indicating that none of the genes plays a role in self-protection
Gene-specific disruption in the filamentous fungus Cercospora nicotianae using a split-marker approach
To determine if DNA configuration, gene locus, and flanking sequences will affect homologous recombination in the phytopathogenic fungus Cercospora nicotianae, we evaluated and compared disruption efficiency targeting four cercosporin toxin biosynthetic genes encoding a polyketide synthase (CTB1), a monooxygenase/O-methyltransferase (CTB3), a NADPH-dependent oxidoreductase (CTB5), and a FAD/FMN-dependent oxidoreductase (CTB7). Transformation of C. nicotianae using a circular plasmid resulted in low disruption frequency. The use of endonucleases or a selectable marker DNA fragment flanked by homologous sequence either at one end or at both ends in the transformation procedures, increased disruption efficiency in some but not all CTB genes. A split-marker approach, using two DNA fragments overlapping within the selectable marker, increased the frequency of targeted gene disruption and homologous integration as high as 50%, depending on the target gene and on the length of homologous DNA sequence flanking the selectable marker. The results indicate that the split-marker approach favorably decreased ectopic integration and thus, greatly facilitated targeted gene disruption in this important fungal pathogen
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